The invention relates to an apparatus for the heat treatment and/or drying of a web of material, consisting of guiding and transporting means for the web of material, of infrared radiators, which are arranged on one of both sides of the web of material at a distance from it and extending over its width and in its longitudinal direction and which can be heated by ducts which are arranged on the rear sides of its radiating plates, have heating medium flowing through them and are adjustable in heating capacity.
It is known to dry webs of material in continuous driers operated with heated air. It is characteristic of this drying that large volumes of air are blown onto the web of material and circulated in the drier housing. In order that the web of material is not adversely affected in its quality by this air blown onto it, the air must be absolutely free from even the smallest foreign bodies. Although this type of drying allows high drying capacities, it also entails disadvantages due to the large volumes of air. Due to the large volumes of air, the parts processing these volumes of air, such as cleaning apparatuses, blowers and the like, must be made correspondingly voluminous.
In order to obviate these difficulties, processes and apparatuses of the type mentioned at the beginning are known in which the exposure to heat of the web of material required for the heat treatment and/or drying takes place by the radiation from infrared radiators.
In the case of a known apparatus of this type (DE 19 19 957 C2), the infrared radiators consist of radiating plates which are heated directly by burners operated with gas and the infrared radiation of which is made uniform by screens arranged between them and the web of material.
In the case of another apparatus of the same generic type (EP 0 157 403 A3), the infrared radiators consist of plates which bear, on their side facing away from the material web, lines, for example for a thermal oil, laid in a snaking form. In order to be able to expose the web of material to a differing radiation capacity over its width, a plurality of line lengths laid in a meandering form are arranged parallel to one another and to the running direction of the web of material. Such an apparatus designed for heating with thermal oil requires a great expenditure in terms of apparatus engineering. A particularly sensitive temperature control cannot be achieved with lines which are laid in a meandering form and through which thermal oil flows.
Finally, infrared radiators for drying ovens are known (DT 1 604 766 A1) of which the radiating element is heated by hot gases conducted over its rear side. In this case, a chamber which is uniform over the entire width of the radiating element is provided for the conduction of the hot gases. In order to be able to effect a differing radiation capacity over the radiating surface in the event of a differing heat requirement, there is provision for influencing the flow rate of the hot gases through the channel taken along the radiating element by means of differing cross-sections. However, due to the then fixed cross-sections, a changing of the thermal radiation of the individual regions of the radiating element in operation is not possible.